1. Field of the Invention
The present invention relates to an optical attenuator using an isolator and an optical communications system including the same. More particularly, the invention relates to an optical attenuator for attenuating an optical beam by imposing a magnetic field change on an isolator, and an optical communications system including the same.
2. Related Art
In optical communications, an optical attenuator is widely employed. The optical attenuator is an important element in various optical components. In particular, when a signal entering via a receiving port during optical transmission is so strong as to go beyond the sensitivity of a detector, the intensity of a signal light can be controlled in accordance with a reception sensing range by including an attenuator.
Typically, an optical attenuator employs an attenuation plate having an attenuation level which varies depending on an angle of rotation thereof. Thus, such optical attenuators require a special motor to rotate the attenuation plate. As a result, the optical attenuator is necessarily large in size and expensive to fabricate. Moreover, the large size of such an optical attenuator prevents it from being easily mounted on or in an optical communications system. Thus, a special mounting device is required, and this further increases the cost of construction of the system.
To solve the above problems, it is an object of the present invention to provide an optical attenuator using an isolator, which can electromagnetically control the attenuation level of the attenuator by controlling the isolation level dependent upon the intensity of a magnetic field applied to the isolator, and an optical communications system including the same.
To achieve the above object, there is provided an optical attenuator using an isolator, which is controls the intensity of an input optical signal. The optical attenuator comprise: an isolator, including a Faraday rotator, in which a polarization rotation angle varies depending on the intensity of an applied magnetic field so as to change the level of isolation of an optical signal according to the polarization rotation angle and to output an attenuated optical signal; a magnetic field generator for generating a magnetic field having an intensity which is controlled by the intensity of current, and applying the generated magnetic field to the isolator; and a power supply for supplying current to the magnetic field generator and for controlling the intensity of the current.
To achieve the above object, there is provided an optical communications system which includes an optical transmitter, first and second optical attenuators, and an optical receiver. Damage to the optical receiver is prevented by controlling the power of an output optical signal of the optical transmitter using the first optical attenuator, and controlling the power of an optical signal to be received by the optical receiver using the second optical attenuator. The first or second optical attenuator comprises: an isolator, including a Faraday rotator, in which a polarization rotation angle varies depending on the intensity of an applied magnetic field so as to change the level of isolation of an optical signal according to the polarization rotation angle and to output an attenuated optical signal; a magnetic field generator for generating a magnetic field having an intensity which is controlled by the intensity of current, the generated magnetic field being applied to the isolator; and a power supply for supplying current to the magnetic field generator and for controlling the intensity of the current.